1. Field of the Invention
The present invention relates to an image processing method in a printing device using a plurality of printing modes with different definition, and in particular, a technique for simplifying image processing including halftone processing.
2. Description of the Related Art
A printer which can change output resolution by switching a printing system without changing a mechanism, such as a printing head, is known, and printing can be performed with resolution of, for example, “1200 dpi (dots per inch)×1200 dpi”, “1200 dpi×600 dpi”, “600 dpi×600 dpi”, and the like. Furthermore, a dot arrangement form as well as resolution can be changed, and printing can be performed in printing modes of various dot arrangement forms (for example, lattice arrangement, zigzag arrangement, and the like).
On the other hand, from the input of image data until printing is performed, there are various kinds of image processing, such as color conversion processing, resolution conversion processing, plate separation processing, unevenness correction processing, and halftone processing. Through a series of image processing based on a printing mode, a desired image is recorded on a printing medium, such as a recording sheet.
JP2012-134968A discloses an image processing device which faithfully reproduces input image data having pixels arranged in a lattice shape with zigzag recording. In the image processing device, a plurality of consecutive pixels in input image data in a direction of reducing the amount of information by half are set as one conversion unit of resolution conversion, the position of the conversion unit matches the phase of zigzag recording, and resolution conversion is performed while shifting between an odd-numbered column and an even-numbered column in input image data in a direction of maintaining the amount of information.
JP2006-186755A discloses an image processing device which reduces storage capacity as a whole. The image processing device includes a module which performs different halftone processing for each of a plurality of aspect ratios of recording resolution, and a module corresponding to one aspect ratio of recording resolution is selected and used to perform halftone processing. With this, even though recording resolution is different, if the aspect ratio is the same, halftone processing is performed using a common threshold matrix.
JP2002-135583A discloses an image processing device having a function of performing image quantization based on an error diffusion method. The image processing device changes an error diffusion coefficient according to output resolution, and for example, decreases an error diffusion range in a case where output resolution is low and increases the error diffusion range in a case where output resolution is high.